A substrate processing apparatus includes a plurality of chambers connected with each other. Among those chambers, there are a transfer chamber, provided in a transfer unit, for transferring a substrate to be processed, e.g., a semiconductor wafer (hereinafter, simply referred to as a “wafer”), between the transfer chamber under the atmospheric pressure and the outside; a vacuum processing chamber for performing a specified process such as etching or film forming process on the wafer; and a vacuum preparation chamber (e.g., load-lock chamber) which is disposed between the vacuum processing chamber and the transfer chamber to be connected with them. The chambers are sealed and connected to each other via gate valves.
In the substrate processing apparatus, the wafer is transferred between those chambers and processed in the vacuum processing chamber. Generally, the wafer is transferred in the substrate processing apparatus including those chambers as follows. For example, the wafer is loaded into the transfer chamber from the outside. Further, the wafer is then loaded into the vacuum processing chamber through the vacuum preparation chamber. Then, a processing such as etching or film forming process is carried out on the wafer in the vacuum processing chamber by using a specified processing gas. When the processing is finished in the vacuum processing chamber, the wafer is transferred back to the transfer chamber via the vacuum preparation chamber. In a wafer transfer between the vacuum preparation chamber and the transfer chamber, once the pressure in the vacuum preparation chamber reaches a specified pressure, for example, by opening the chamber to the atmosphere, the gate valve between the chambers is opened and the wafer is transferred between the vacuum preparation chamber and the transfer chamber. Further, in a wafer transfer between the vacuum preparation chamber and the vacuum chamber, once the vacuum preparation chamber reaches to a predetermined pressure, for example, by vacuum processing, the gate valve between the chambers is opened and the wafer is transferred between the vacuum preparation chamber and the vacuum processing chamber. In other words, when the wafer is transferred between the chambers, each chamber is controlled to set its pressure at a specified value in order to reduce a pressure difference between the chambers.
However, depending on a pressure condition of each chamber, when the gate valve is opened between the chambers, there give rise to various problems such as a processing gas remaining in the vacuum processing chamber flowing backward; contaminant such as water being introduced from the transfer chamber; and particles (deposits, dust and the like) being swirled up in the chambers. Accordingly, the wafer may be contaminated by the particles or contaminant. Further, when a corrosive processing gas flows backward into another chamber, the components in the chamber may be corroded.
Thus, conventionally, before the gate valve is opened, a pressure in the chamber is controlled in many ways. For example, in case that the vacuum preparation chamber is opened to the atmosphere when the gate valve between the transfer chamber and the vacuum preparation chamber is opened, the vacuum preparation chamber is evacuated while supplying a purge gas such as N2 gas thereto for the purpose of removing the particles present in the vacuum preparation chamber in advance (see, e.g., Japanese Patent Laid-open Publication No. H3-087386).
Further, in a so-called cluster tool type substrate processing apparatus, wherein a plurality of vacuum processing chambers are connected to a common transfer chamber and a vacuum preparation chamber (load-lock chamber) is connected to the common transfer chamber, when a gate valve between the common transfer chamber and one of the vacuum processing chambers or between the common transfer chamber and the load-lock chamber is opened, a pressure of the common transfer chamber is made slightly higher than that of the vacuum processing chamber or the load-lock chamber by supplying a purge gas such as N2 gas to the common transfer chamber, thereby forming a gas flow from the common transfer chamber to the vacuum processing chamber or the load-lock chamber. Accordingly, a processing gas or contaminant such as water is prevented from flowing into the common transfer chamber (see, e.g., Japanese Patent Laid-open Publication No. H7-211761)
However, in the aforementioned conventional technology, in order to prevent the backflow of the processing gas and cross contamination and to remove the particles, the pressure of the relevant chamber is controlled by supplying the purge gas such as N2 gas to thereby cause a pressure difference between the chambers.
Depending on the pressure difference between the chambers, a gas flow is generated when the gate valve is opened, and particles are swirled up along the flow in the chamber. Particularly, when the pressure difference between the chambers is large, a shock wave (very strong pressure wave which is transmitted at a supersonic speed when compressible fluid flows at a high speed) is generated and along the propagation of the shock wave, the particles will be swirled up in the chamber.
Thus, by slightly reducing the pressure difference between the chambers, one may expect to prevent the swirling up of particles. But, recently, airtightness of the chambers is further enhanced due to improvement in sealing technology. Accordingly, in the conventional sequence of pressure control, the inner pressure of the chamber becomes needlessly high due to, e.g., the introduction of the purge gas, thereby needlessly increasing an actual pressure difference between chambers.
Further, it may be possible to accurately control the pressure of each chamber such that the pressure difference between chambers does not become excessively high by precisely measuring the pressures of all chambers. However, in order to accurately control the pressure, an expensive pressure gauge or a control apparatus is required to thereby increase the cost and, further, it is not practical because the sequence of the pressure control becomes too complicated.
Further, Japanese Patent Laid-open Publication No. H7-211761 discloses that a bypass capable of being opened or closed is provided between the chambers and the bypass is opened before the gate valve is opened to reduce the pressure difference between the chambers, whereby forming a rapid flow of gas (pressure wave) is prevented when the gate valve is opened. However, when the bypass is opened, depending on the pressure difference between the chambers, a shock wave may be generated even before the gate valve is opened and propagate into the chamber, thereby making particles be swirled up.